Rare earth element has wide application. In the 1960's, Chinese scientists first used rare earth complex as polymerizing catalyst. Research has shown that neodymium element has the highest polymerizing activity, thus, the rare earth with high content of neodymium element is frequently used as polymerizing catalyst. Because rare earth has similar qualities and is hard to separate, in the field of polymerizing catalyst, neodymium catalyst is commonly called rare earth catalyst, while neodymium chloride complex is commonly called rare earth chloride complex. Most rare earth chloride complexes are synthesized from anhydrous rare earth chloride; only very few may be synthesized from rare earth chloride with crystal water in ethanol. Therefore, most rare earth chloride complex synthesis is inconvenient and costly.
Rare earth chloride complex is insoluble in nonpolar carbon-hydrogen solvent. Rather, they can only be used in a solid form, thus the effective utilization ratio of rare earth chloride complex is very low. Due to the insolubility of rare earth chloride-ethanol complex in aliphatic hydrocarbon solvent, its effective utilization ratio is merely 0.7% when rare earth chloride-ethanol complex is used as a catalyst component for catalyzing the polymerization of diene (Rare Earth Catalyst and Polymerization, Jun Ouyang, p. 143).
The most effective way to improve the effective utilization ratio of rare earth chloride complex is to improve the dispersibility of rare earth chloride complex so as to achieve homogeneous phase dispersion. At the same time, a key technique to lower the synthesis cost and to simply the synthesis process is to avoid using anhydrous rare earth chloride as the raw material to produce rare earth chloride complex. Researchers worldwide have conducted extensive research to solve these problems, but still failed to avoid using anhydrous rare earth chloride as the raw material, thus failed to produce rare earth chloride complex that is soluble in aliphatic hydrocarbon solvent.
Researchers outside China first dissolved anhydrous rare earth chloride in tetrahydrofuran polar solvent, then dropped such solution into hexane with high-speed stirring to produce rare earth chloride complex nanoparticles. (Kwag G., Kim D., Lee S., Bac C., Morphology and Activity of Nanosized NdCl3 Catalyst for 1,3-Butadiene Polymerization, J. Appl. Polym. Sci., 2005, 97:1278-1283.). Although such complex may be made into nanoparticles, it is still insoluble, and further, a large amount of tetrahydrofuran was used during the synthesis, causing an environmental problem.
Chinese researchers used anhydrous rare earth chloride to produce higher alcohol complex. Such complex may be in a form of semitranslucent colloid in carbon-hydrogen solvent (Investigation on the reactive features of isoprene polymerization from rare earth complex, Changyou Ren, M. S. thesis of Chinese Academy of Sciences). The anhydrous rare earth chloride-higher alcohol complex dispersed in hexane and formed colloid. However, precipitation was observed after three days, which means that it was not truly dissolved in hexane.
Rare earth chloride-tributyl phosphate complex is soluble in aromatic hydrocarbon solvent (EP 0994131A1), but it is produced from anhydrous rare earth chloride. Although rare earth chloride-neutral phosphate complex may be produced from rare earth chloride with crystal water (The catalytic activity of the rare earth compound with different coordination groups in polymerization of isoprene, Wenqi Chen, Essays of rubber synthesis catalyzed by rare earth. p. 113), aromatic hydrocarbon is used as a solvent in the synthesis process, and aromatic hydrocarbon is widely known for its severe toxic effect on the environment.